In network interface card (NIC) terminology, the terms “fail open” and fail safe” are often used differently than in the terminology of electrical switches. When a firewall “fails open”, it appears like a door which is blocked or propped open so that all network traffic flows through the firewall unimpeded (and unchecked). If an electrical switch “fails open”, it does not provide a complete electrical path between the poles, so no signal passes through it (e.g., antonymous from the network interface usage).
Similarly, when a NIC “fails closed”, it is thought of as a closed door, thus unselectively blocking all traffic through it. But, when an electrical switch fails closed, it provides an uninterrupted electrical path between the poles of the switch.
For the purposes of this disclosure, we will be using the network interface definitions of these terms, not the electrical circuit definitions, whereas the invention relates not to the physical layer of a communication stack (e.g., metallic, optical, wireless, etc.) such as layer 1 of the seven-layer Open System Interconnection (OSI) model, but to the layers above the physical layer. In order for a network interface device such as a router, firewall, etc., to “fail open”, it must actively conduct formatted data, not just electrical signal, such as layers 2 through 6, e.g., data link, network, transport, session and presentation layers, respectively. As such, in this manner of usage, “failing open” and “failing closed” is more of a functional and operational mode than it is an electrical conductivity state.